Although a conventional aromatic polycarbonate resin containing a structure originating in bisphenol A, etc. is produced by using a raw material derived from petroleum resources, in recent years, depletion of petroleum resources is concerned, and it is demanded to provide a polycarbonate resin using a raw material obtained from biomass resources such as plant. In addition, because of a concern that global warming due to increase or accumulation of carbon dioxide emissions may bring about climate change, etc., development of a polycarbonate resin using a plant-derived monomer as a raw material and being carbon neutral even when discarded after use is demanded.
Under these circumstances, there has been proposed a method where isosorbide (ISB) which is a dihydroxy compound obtained from biomass resources is used as a monomer component and a polycarbonate resin is obtained through transesterification with a carbonic acid diester with distilling off a by-produced monohydroxy compound under reduced pressure (see, for example, Patent Documents 1 to 7).
However, a dihydroxy compound such as ISB has low thermal stability, in comparison with bisphenol compounds used for a conventional aromatic polycarbonate resin, and there is a problem that the resin is colored through thermal decomposition at the time of polycondensation reaction, molding or processing, which are performed at a high temperature. Furthermore, as for the copolymer of ISB and a bisphenol compound described in Patent Documents 3 to 6, although a polymer having a high glass transition temperature is obtained, on the other hand, the terminal of the polymer becomes a bisphenol compound due to a difference between the reactivity of ISB and the reactivity of a bisphenol compound and when a polymerization temperature lower than the polymerization temperature of an aromatic polycarbonate resin is selected in consideration of color tone or thermal stability of ISB, a kind of end capping occurs, as a result, the polymerization degree may not sufficiently increase, resulting in a polymer having poor impact resistance. This is conspicuous particularly when the copolymerization amount of a bisphenol compound in the polymer is 20 mol % or more.
Furthermore, Patent Document 7 discloses a polycarbonate copolymer containing a constitutional unit derived from ISB, a constitutional unit derived from an aliphatic dihydroxy compound, and a constitutional unit derived from an aromatic bisphenol compound. However, this polycarbonate copolymer also contains a constitutional unit derived from a bisphenol compound and although the heat resistance, moldability and mechanical strength are excellent, the degree of polymerization may not sufficiently increase, resulting in a polymer having poor impact resistance. In addition, the biogenic substance content rate is low, and this is unfavorable in view of environment.
A polycarbonate resin composed of a dihydroxy compound such as isosorbide (ISB) that is a dihydroxy compound obtained from biomass resources, has a high glass transition temperature and excellent heat resistance but is rigid and moreover, has drawbacks of high melt viscosity at the time of melt polymerization and poor impact resistance because polymer having a high molecular weight cannot be obtained. In order to improve toughness, attempts are being made to copolymerize an aliphatic dihydroxy compound or an aromatic bisphenol compound.
Specifically, Patent Document 8 discloses a polycarbonate resin composition containing a polycarbonate resin and an aromatic polycarbonate resin, wherein the polycarbonate resin contains a constitutional unit derived from ISB and a dihydroxy compound of an aliphatic hydrocarbon and the content of a constitutional unit derived from the dihydroxy compound of an aliphatic hydrocarbon is 45 mol % or more. Patent Document 9 discloses a polycarbonate resin composition having excellent pencil hardness, which is obtained by mixing an aromatic polycarbonate resin with a polycarbonate resin containing a constitutional unit derived from ISB and a dihydroxy compound of an aliphatic hydrocarbon.